Temperature control system having means to measure turbine inlet temperature indirectly



J. A. DRAKE June 9, 1953 2,641,105 TEMPERATURE CONTROL SYSTEM HAVING MEANS TO MEASURE TURBINE INLET TEMPERATURE INDIRECTLY 3 Sheecs-She'et 1 Filed Oct. 11, 1948 30&

INVENTOR. JOHN A. DRAKE ATTORNEYS June 9, 1953 J. A. DRAKE 2,641,105

TEMPERATURE CONTROL SYSTEM HAVING MEANS T0 MEASURE TURBINE INLET TEMPERATURE INDIRECTLY Filed Oct. 11, 1948 3 Sheets-Sheet 2 (EOHW JPI 32 m (T MNN,

INVENTOR. JOHN A. DRAKE BY v v ATTORNEYS June 9, 1953 Filed 001;. 11. 1948 A. DRAKE 2,641,105 TEMPERATURE CONTROL SYSTEM HAVING MEANS TO MEASURE TURBINE INLET TEMPERATURE INDIRECTLY I 3 Sheets-Sheet 3 [J1] III IIIIIIIII ll 1 l I THE/P4108717 INVENTOR. JOHN A. DRAKE ATTORNEYS Patented June 9, 1953 TEMPERATURE CONTROL SYSTEM HAVING MEANS TO MEASURE TURBINE INLET TEMPERATURE INDIRECTLY John A. Drake, Los Angeles, Calif., assignor to Marquardt Aircraft Company, Van Nuys, Calif., a corporation of California Application October 11, 1948, Serial No. 53,791

12 Claims.

This invention relates to a temperature control system. More particularly, it relates to a temperature control system which is operable to control the turbine inlet temperature of a turbojet engine or of any other engine wherein heat is added to a working fluid in a combustion chamber, and wherein the duct ventingthe fluid from the combustion chamber is choked.

The invention will first be described with reference to a turbojet engine and its applicability to other engines will be discussed thereafter.

As is well known, a turbojet engine comprises an airframe within which is disposed a compressor, combustion chambers, a turbine, a shaft connecting the turbine and the compressor and an exit nozzle. The outlets of the combustion chambers are choked, i.e., they are of convergentdivergent longitudinal section, so as to accelerate the gases at the turbine inlet. The turbine, besides driving the compressor, may also drive a propeller, and further work is obtained by venting the gases from the turbine through an exit nozzle to obtain a thrust.

In turbojet engines, temperature control at the turbine inlet is important. Thus, with present materials of construction, the turbine inlet temperature should not exceeed about 1500 F.; otherwise, the blades will burn off. But from the standpoint of jet efliciency, a turbine inlet temperature as near 1500 F. as possible should be maintained.

It is apparent that, to achieve maximum efflciency yet avoid mechanical failure, a temperature control system is required which is dependable and accurate and which responds rapidly to changing conditions.

Systems employed heretofore have involved too great a time lag to be satisfactory, or have been inaccurate. Thus, in some cases the time lag has been such as to result in structural damage before the faulty condition has been corrected. Inaccuracies result from such phenomena as the velocity of flow past the thermal element used to measure the critical temperature, radiation from local hot spots, and variation of temperature across the critical region.

Such methods as have been used heretofore have measured the critical temperature more or less directly, resulting in the inaccuracies noted above. Direct measurement of temperature under the conditions prevailing at the inlet of a jet turbine is exceedingly difficult to carry out accurately and rapidly; and rapid translation of such measurement into a mechanical control is likewise exceedingly difllcult.

It is an object of the present invention to provide an improved temperature control system for jet engines and other engines wherein heat is added to a working fluid in a combustion chamber and the heated fluid is vented through a choked duct.

It is a further object of the invention to provide an indirect means of measuring temperatures in engines of the character described.

It is a still further object of the invention to provide means of measuring high temperatures at choked exit ducts, such as at the turbine inlet of a turbojet engine, without direct measurement of the temperature at such point, such means being accurate and involving very little time lag.

It is a particular object of the invention to provide a temperature control system for turbojet engines and the like which is rapidly and accurately responsive to temperature variations at critical areas and is operable rapidly to correct conditions to control such temperature.

These and other objects of the invention will be apparent from the ensuing description and the appended claims.

Certain forms which the invention may assume are exemplified in the folowing description and illustrated by way of example in the accompanying drawings, in which:

Fig. 1 is a schematic view of a conventional turbojet engine showing diagrammatically only those parts which are essential to an understanding of the invention.

Figs. 2 and 3 are schematic representations of a mechanical system and an electrical system, respectively, each operative tocontrol the turbine inlet temperature.

Fig. 4 .is a schematic representation of. an alternative mechanical control system.

Referring now to Fig. 1, the numeral III indicates generally a turbojet engine comprisingan air frame II, a compressor l2, combustion chambers l3 each having a choked or convergent divergent nozzle [3a, a turbine l4 and a shaft l5 operatively connecting the turbine and compressor. Also shown are a fuel inlet [6, a nozzle section 20 and mechanical means'25, such as vanes pivotally supported at 26, for varying the nozzle area. A linkage 21 is provided for actuating the vanes 25.

The turbojet I0 is also provided with a con duit opening upstream at the compressor inlet, a conduit 3| opening upsteam at the compressor outlet and a conduit 32 also opening into the compressor outlet but in a direction transverse to the air stream, as shown. The purpose.

3 of the conduits 30, 3| and 32 is explained hereinafter.

I have discovered that, in the critical operating range, i. e., at high engine R. P. M. and at high turbine inlet temperature, the turbine inlet temperature can be measured indirectly by measuring two pressures and a low temperature.

Before elaborating this point, certain terms will be defined, as follows:

Tt is the total temperature; 1. e., temperature as measured in an air stream when the air is brought to rest.

Pt is total pressure; 1. e., pressure as measured through a duct opening intoan air stream.

P is a static pressure; i. e., pressure as moasured by the static pressure orifice of a pitot-static tube.

N is the R. P. M. of the turbine.

k and C are constants.

subscripts 0, l and 2, as in the terms Tt Pt Pi and 'Tt indicate values iof'the terms 'Tt, Pt and P at the compressor inlet of -ZB'ig. 1, at the .com-

.pressor outlet or combustion chamber inlet and 'at the turbine inlet, respectively.

Mathematically stated, the discovery set forth hereinabove is as follows:

Tt is a function are two pressures, turbine R. P. M. and a *low temperature, each :of which can be easily, rapidly and accurately measured. By employinglarge pressure lines, the lag in' mea'suring these variables' can be made almost vanishingly small, and none of them varies rapidly. Thus, Tt varies'only with altitude and flight speed, hence does not vary rapidly, 'and its measurement is not'an'ected by' radiation and 'temperature gradient errors affecting the :direct measurement of Tt Equation 1 contains, it will be noted, the term T: +'kN". This term is an approximation which is sufficiently accurate for practical purposes. A more rigorous derivation would employ the term Tt hence, Equation 1 would "become This equation is simpler, as it involves one less unknown quantity. The quantity Tt like Ti in Equation 1, is the only temperature measured, and although it is a higher temperature than Ta it is a much lower temperature and is much more easily measured than Tt Referring now to Fig. 2 of the drawings, the conduits 30, 3| and '32 have the same significance as in Fig. 1. A lever '35 is provided having a variable fulcrum 36 and arms 135a and 351') whose lengths are determined :by the position of the fulcrum '36. The arm 85a is connected by a rod 31 to a bellows 38 disposed in agas tight chamber 39. The pressure Pl is'communicated to the interior of bellows 58 through a conduit 32a and the pressure Pt, is communicated to the chamber v39 outside the bellows through the conduit 31.

It will be seen that an upward force will be exerted on the arm Slim-which is proportional-to Pz P1, thus providing the denominator of the right hand side of Equation 1.

In the fuel line I6 of the turbojet fuel pump (not shown), there is provided a convergentdivergent section 40 which is tapped at its inlet and 'at'its throat by conduits 4| and 42, respectively, as shown. These conduits communicate with opposite sides of a flexible diaphragm 43, which is connected by a rod 44 to the metallic diaphragm 45 of a thermal expansive unit 45a. The duct 30 is in thermal communication with the thermal expansive unit as shown, and is vented through a conduit 30a. The diaphragm 45 -is-;connected to a needle valve 46.

As indicated, the force actuating the needle "valve '46 is the sum of two forces, To, and kN acting in the direction indicated by the arrow. The pressure P1 must be multiplied by the term Tz +lcN to provide the numerator of the right hand side of Equation 1.; This is accomplished by means of a pressure multiplying device 41, as more fully described in my co-pending app1ica-= tion, Serial No. 53,792,.filed October 11, 1948, entitled Pressure :Control Device.

Briefly, the pressure multiplying device 4 1 comprises a gas tight chamber H0 and a flexible diaphragm .l H and a bellows "I I2 disposed therein as shown. The duct 32b provides the inlet, and a duct 320 provides the outlet, and a choked or convergent-divergent section 113 is disposed in the inlet duct 32b and a similar section I I4 is disposed in the outlet duct 320, as shown. As illustrated, the needle valve 48 controls the throat area, Sb,'l0f:' the section H3. As more fully e20 plained i-n-my said cospending application, section 4141s larger than section 1 l3 for theoperating conditions-of turbojets wherein the. ratio of pressure across the-two sections causes-sonicflow at the throat, and-supersonic flow in, the

divergent portion of each section. v i

,As explained in greater detail in my co-jpend:

and that, as a consequence, a downward force is exerted on the arm 35?) of the lever 35 which is proportional to The force (Tt.,+kN )P., translates the fulcrum 36 .to the left or right; the distance is proportional to the force since the bellows H2 acts as a spring. Lever 35a is a first class lever. The

displacement of the fulcrum changes the ratio,

of the lever arms. The displacement up or down of one end is the product the displacement of the other end times the ratio of the lever arms Therefore, lever 35a acts as a multiplier; itmultiplies the quantity (Pt,P,) by the lever arm ratio. A downward force on arm 35b and rod 56 proportional to T -l-kN P -:1) l

is therefore exerted. I To transmit and amplify this force to actuate the vanes 25, a servo piston 55 is providedand is connected to the arm 35b by a rod 56. The servo piston 55 is provided with the usual cylinder 51, hydraulic pressure line 58 and sump lines 59 and with lines 60 and SI communicating with opposite sides of an actuator piston 62 reciprocable in a cylinder 63. The piston 62 is connected by a rod 64 and the rod 21 to the vanes 25. An operating rod or lever 65 is also provided which is manually operable to vary the compression on a coil spring 65 compressed between a collar 61 on the rod 55 and a collar 68 secured to the rod 65. By setting the rod 65 at the desired value of T11 as indicated by a suitable calibrated scale (not shown), any desired turbine inlet temperature can be maintained. The rod 65 can, of course, also be used by an operator, such as a pilot in a piloted craft, to override the automatic control.

Referring to Figure 3, a resistor 12 is connected to a source of constant voltage 100., the other terminal of the constant voltage source is connected to ground. The resistor 12 is enclosed in a thermally insulated chamber I3 in communication with duct 30. A vent 30a is also provided. The voltage drop from the constant voltage source 10a. to the lead 'IIa is proportional to the resistance of resistor I2, which in turn is proportional to T1;,,. Hence as indicated, the voltage from lead Ila to ground is proportional to Tt To this is added a voltage proportional to N in the following manner:

A spring loaded centrifugal flyweight I is driven through any suitable mechanical connection indicated generally as 14 by the turbine shaft I5. Through a link 150., the flyweight I5 actuates the arm I0 of a linear potentiometer Ilia connected to a source of constant voltage by a lead II. It is thus apparent that a voltage from lead I! to ground proportional to N or the square of the rotary speed of the turbine I4, is tapped from the potentiometer lfia. As indicated, the voltage from lead 11 to lead I Ia. is the sum of two voltages, each proportional to Ta, and N respectively. Leads TI and Ha are connected to either end of a linear potentiometer I9, having an arm 80. The arm 80 is actuated by a rod 8| connected to an evacuated bellows 82 housed in a chamber 83. Chamber 83 is in communication with a conduit 32, hence the voltage between lead 84 and lead I la is proportional to the product of P1 and the quantity Tt +kN This voltage is divided by a factor proportional to Fif -P1 by means of a linear potentiometer 85 having an arm 86 which is actuated by the rod 88 connected to a bellows 90. The bellows 90 is housed in a chamber 9|, and conduit 32 communicates with the interior of the bellows through a branch conduit 32a, while conduit 3| communicates with the chamber 9| outside the bellows. It is, therefore, apparent that the voltage between lead 92 and lead Ila is proportional to T -l-kN P '1 P1 From Equation 1 it is seen that the voltage between leads 92 and I la is proportional to the total temperature (Tg) existing at the turbine inlet nozzle I3a. If this voltage were placed across a voltmeter, Tr, could be read directly from a suitably calibrated scale. However, since the purpose of this system is to automatically regulate Tr, to a selected value, the circuit in Figure 3 i com- 6, plated through a circuit responsive to th difference between the actual Tr, and the desired value of Ta, and a means to actuate exit nozzle vanes which when moved will change the operating conditions of the turbine, and hence cause the actual Tr, to equal the desired Ts. To select the desired value of Te, the arm 95 of a potentiometer 94 is manually operated by means of a control lever 96 and linkage 91. The potentiometer 94 is placed across a source of constant voltage 10?). Thus, the voltage between lead 98 and lead 93 is proportional to the control lever setting, which is suitably calibrated with a scale of values of desired Ta. Leads Ho and 98 are connected. Leads 92 and 93 are connected. Thus the voltage between leads I 0| and I02 is proportional to the difierence between the desired temperature T15 and the actual temperature Tt A power amplifier I00 of known type is connected by any suitable electrical, mechanical or hydraulic linkage I03 of known type with a suitable linear actuator I04 of known type to control the vanes 25. The vanes 25 are thus repositioned to the proper position such that the actual Tr, equals the desired Tt Referring now to Fig. 4, there i shown a mechanical control system which, unlike that of Fig. 2, controls fuel flow rather than the exit nozzle and which solves Equation 2, i. e.,

an Til-K A fuel duct I6 and gas sampling ducts 3| and 32 are provided as in the case of Fig. l. A pressure multiplying device I20 is also provided comprising a gas tight chamber I 2|, and a flexible diaphragm I22 and bellows I23 and I24 are disposed therein as shown. The diaphragm is thus divided into a central area S1 exposed to the interior of both bellows and an annuular area S2 external to the bellows. The annuluar space I21 is evacuated and the bellows I23 communicates with a branch duct 3I a, thus communicating a pressure Pt, to that bellows and to the diaphragm area S1. Duct 32 communicates with bellows I24, thus communicating pressure P1 to that bellows and to the opposite side of the diaphragm area S1. It will thus be seen that a net force is applied to the diaphragm I22 which is equal to P: P1.

A branch duct 32a having a choked or convergent-divergent section I28 opens into the annular space I29, which is vented through a duct i 30 having a choked or convergent-divergent section I3I. A needle valve I40, which controls the throat area of the section I3I, is actuated by a thermal expansive unit I4I comprising a metallic diaphragm I42 whose expansion and contraction are determined by the temperature Tt by exposure to gas entering the unit through a duct 3Ib and leaving through a duct I43.

From the discussion above, with reference to Fig. 2, it will be apparent that the pressure in the annular space I29 will be proportional to T .P1. The diaphragm areas S1 and S2 are so chosen that, when the forces on the diaphragm are in balance, Equation 3 is satisfied:

From this and from Equation 2, Equation 4 follows:

As also shown in Fig. 4, a valve I50 is provided inthe fuel line, it and is actuated, through a valve stem lfl', by the diaphragm E22. It will, therefore, be apparent that, should IE drop below the desired value, the resulting unbalance of iforces acting on the diaphragm i212- will open the valve E50 wider. Conversely, if Tt exceeds the desired value, the valve PM will be moved toward closed position. In either case, the fuel flow will be throttled to restore the system to the desired operating conditions.

Means is also provided for setting the control system of Fig. 4 at any desired value of Tt Thus, as shown, the duct 3m opens into bellows in through a convergent-divergent section I52 and a vent E53 is provided also having a convergentdivergent section I54, which is controlled by a needle valve I55. Similar means are provided for the bellows lid, as shown, including a choked section I56 in inlet duct 32, and an outlet duct 4157 having a choked section 58 controlled by a needle valve I59. Both needle valves :55 and 259 are controlled by a control lever 55 through links 168. It? and bell crank levers I88, H59, such thatv the needle valves i5 5 and i239 are moved together an equal amount to open or closethe throats of the sections I54 and Hill. It will be apparent that, by moving control lever 165, the force on diaphragm in (which is proportional to the value of Pt -PL)- Thus, the lever H55 can be set to maintain the turbine inlet temperature, Tt at any desired value.

There have been thus described three systems for controlling turbine inlet temperature of a turbojet. by automatic and indirect means. Other systems will be apparent to one skilled in the art. and it will also be apparent that the same principles and means are applicable in the case of; any engine of the through flow type, wherein heat is added to a working fluid, as by combustion in a combustion. chamber, and the hot fluid is vented through a. convergent-divergent or choked duct where it attains sonic velocity or a Mach number of unity.

It will, therefore, be apparent that the control system is applicable to a ram jet engine, to any gas turbine satisfying the criteria mentioned, and to all engines of the type mentioned whether useful work is taken in the form of thrust of a jet as in the nozzle of a jet engine, or as the kinetic energy of a turbine, which may drive a propeller. wheels, etc. It will also be apparent that the temperature controlled, i. e., the temperature of gases from a choked exit duct of a combustion chamber, may have an optimum value varying within a wide range and dependout upon a particular set of circumstances. Also, instead of controlling such temperature by controlling the area of an exit nozzle or the flow of fuel, it may be controlled by other means such as varying the pitch of a propeller or the back M. F. of a generator.

While I have shown the preferred form of my invention, it is to be understood that various changes may be made in its construction by those skilled in the art without departing from the spirit of the invention as defined in the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

l. A control system for a turbojet engine hav ing in flight a compressor inlet temperature of Tt a compressor outlet total and static pressure of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Ta, said system comprising pressure responsive means ineluding a pitot tube and a static tube responsive respectively to Pt, and P1, and exerting a first force proportional to Pt P1,, means responsive to Tr, and N and exerting a second force proportional to Tt +kN where k is a constant, means responsive to said second force and to P1 and exerting a third force proportional to (T: +I :N ),P1, and means for dividing said third force by said first force to obtain a force proportional to Ta.

2. A control system for a turbojet engine having in flight a compressor inlet temperature of Tt compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Tt said system comprising means responsive to Pt, and P1, and exerting a first force proportional to P: P1, means responsive to Tt and N and exerting a second force proportional to T1,, +lcN where k is a constant, means responsive to said second force and to P1 and exerting a third force proportional to (Tr +kN )P1, means for dividing said third force by said first force to obtain a force proportional to Te settable means for bucking the last named force in accordance with the manner of setting the settable means, and means for applying the resultant force to control the inlet temperature of the turbine.

3'. A control system for a turbojet engine having in flight a compressor inlet temperature 01 Tr a compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Tt said system comprising pressure responsive means including a pitot tube and a static tube responsive respectively to Pt, and P1, and exerting a first force proportional to Fr -P1, means responsive to T15 and N and exerting a second force proportional to Tz -l-kN where k is a constant, means responsive to said second force and to P1 and exerting a third force proportional to (Tt +-kN )Pl, and means for dividing said third force by said first force to obtain a force proportional to Th and settable means for bucking the last named rorcc in accordance with the manner of setting the settable means, and means for applying the resultant force to control the inlet temperature of the turbine.

4. A control system for a turbojet engine having in flight a compressor inlet temperature of T1,, a compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Ta, said system comprising means responsive to Pt, and P1, and exerting a first force proportional to P,P1, means responsive to Tr, and N and exerting a second force proportional to Tt +kN where k is a constant, the last named means including a pres sure responsive means responsive to N connected in tandem with a temperature responsive element responsive to Tt means responsive to said second force and to P1 and exerting a third force proportional to (Tt +kN )Pl, and means for dividing said third force by said first force to obtain a force proportional to Ta.

5. A control system for a turbojet engine having in flight a compressor inlet temperature of Tt a compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Tt said system comprising pressure responsive means including a pitot tube. and a static tube responsive respectively to Pr, and P1, and exerting a first force proportional to Pt -P1,. means responsive to Tr, and N and exerting a second force proportional to Tt +kN where k is a constant, the last named means including a pressure responsive means responsive to N connected in tandem with a temperature responsive element responsive to Tt means responsive to said second force and to P1 and exerting a third force proportional to (Tt +7N )Pl, and means for dividing said third force by said first force to obtain a force proportional to Te.

6. A control system for a turbojet engine having in flight a compressor inlet temperature of Tt a compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of T1;,,, said system comprising means responsive to Pt, and P1, and exerting a first force proportional to Pr,P1, means responsive to Ta, and N and exerting a second force proportional to Tt +kN where k is a constant, the last named means including a pressure responsive means responsive to N connected in tandem with a temperature responsive element responsive to Tt means responsive to said second force and to P1 and exerting a third force proportional to (Tt +kN )Pl, and means for dividing said third force by said first force to obtain a force proportional to Ta, and settable means for bucking the last named force in accordance with the manner of settin the settable means, and means for applying the resultant force to control the inlet temperature to the turbine.

7 A control system for a turbojet engine having in flight a compressor inlet temperature of Tt a compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Tt said system comprising pressure responsive means including a pitot tube and a static tube responsive respectively to P1,, and P1, and exerting a first force proportional to Pt P1, means responsive to Tr, and N and exerting a second force proportional to Tr -l-kN where k is a constant, the last named means including a pressure responsive means responsive to N and connected in tandem with a temperature responsive element responsive to T1,, means responsive to said second force and to P1 and exerting a third force proportional to (Tt +kN )P1, means for dividing said third force by said first force to obtain a force proportional to Tg, settable means for bucking the last named force in accordance with the manner of setting of the settable means, and means for applying the resultant force to control the inlet temperature to the turbine.

8. A control system for a turbo-jet engine having mechanically operable means for governing turbine inlet temperature and having in fiight a compressor inlet temperature of Tt compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Ta, said system comprising hydraulic means for actuating said governing means and control means for said hydraulic means, said control means comprising means responsive to Pt, and P1, and exerting a first force proportional to Fr -P1, means responsive to Ta, and N and exerting a second force proportional to T +7cN where k is a constant, means responsive to said second force and to P1 and exerting a third force proportional to (Tr +kN )P1, means for dividing- 10 turbine inlet temperature and having in flight a compressor inlet temperature of Tt compressor outlet and total static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Te, said system comprising hydraulic means for actuating said governing means and control means for said hydraulic means, said control means comprising pressure responsive means including a pitot tube and a static tube responsive respectively to Pt, and P1, and exerting a first force proportional to Pt -P1, means responsive to Ta, and N and exerting a second force proportional to Tt,+kN where k is a constant, means responsive to said second force and to P1 and exerting a third force proportional to (Tt +7CZV )P1, means for dividing said third force by said first force to obtain a force proportional to Tg, and mechanical means responsive to the last named force for actuating said hydraulic means.

10. A control system for a turbojet engine having mechanically operable means for governing turbine inlet temperature and having in flight a compressor inlet temperature of Tt compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Te, said system comprising hydraulic means for actuating said governing means and control means for said hydraulic means, said control means comprising means responsive to Pt, and P1, and exerting a first force proportional to Fr -P1, means responsive to Tc, and N and exerting a second force proportional to Tt +kN where k is a constant, means responsive to said second force and to P1 and exerting a third force proportional to (Tr +kN P1, means for dividing said third force by said first force to obtain a force proportional to Tt settable means for bucking the last named force in accordance with the manner of setting the settable means, and mechanical means for applying the resultant force to actuate the hydraulic means.

11. A control system for a turbojet engine having in flight a compressor inlet temperature of Tt compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of T11 said system comprising means responsive to Pt, and P1, and exerting a first force proportional to Pt,-P1, means responsive to Tr, and N and exerting a second force proportional to Tr +7cN where k is a constant, means responsive to said second force and to P1 and exerting a third force proportional to (Tt,,+kN P1, and means for dividing said third force by said first force to obtain a force proportional to Tt 12. A control system for a turbojet engine having mechanically operable means for governing turbine inlet temperature and having in flight a compressor inlet temperature of Tw compressor outlet total and static pressures of Pt, and P1, a turbine rotary speed of N and a turbine inlet total temperature of Ta, said system comprising hydraulic means for actuating said governing means and control means for said hydraulic means, said control means comprising pneumatic means responsive to Pt, and P1 and exerting a first force proportional to Fr -P1, a thermal expansive member responsive to Ta, and exerting a second force proportional thereto, pneumatic means responsive to fuel flow and exerting a, third force proportional to N pneumatic means responsive to P1 and to the sum of said second and third forces and exerting a fourth force proportional to (Tt +kN P1, and mechanical means respon- 11 sive to said first and fourth forces for exerting Number on said hydraulic means a fore proportional to 2,411,895 2 427 835 2 .v 1 (To 7 2,457,595 4 P. 1 5 2,463,566 JOHN A. DRAKE. 2,479,813 2,559,623 References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date 560,196

Lundgaard May Name Date Poole 3, 1946 Campbell Sept. 23, 1947 Orr Dec. 228, 1948 Saldin .o Mar. 8, 1949 Chamberlin Aug. 23, 1919 Holmes July 10, I951 FOREIGN PATENTS Country Date Great Britain Mar. 24, 1944 

